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What is the `volatile` keyword in Java?

In Java, the volatile keyword is used to ensure the visibility of variables in a multi-threaded environment. Its core purpose is to ensure that the latest write value can be obtained during reading. When a variable is declared as volatile, the JVM will prohibit the variable from being cached locally in each thread, forcing all read and write operations to occur in the main memory, thereby avoiding inter-thread communication problems caused by cache inconsistency. It is suitable for the following scenarios: 1. Variables are accessed by multiple threads; 2. The update of variables does not depend on the current value (such as no composite operations such as self-increase are involved); 3. Atomic guarantee is not required. Typical use cases include status flags, one-time safe releases, and weak state synchronization. Unlike synchronized, volatile only provides visibility

Jul 06, 2025 am 02:02 AM

java volatile

Difference between interface and abstract class in Java.

Useabstractclassestosharecodeanddefinenon-staticfields,whileinterfacesdefinecontractsandsupportmultipleinheritance.1.Abstractclassesallowbothabstractandconcretemethods,interfacesonlyabstract(beforeJava8)ordefault/staticmethods(Java8 ).2.Abstractclass

Jul 06, 2025 am 02:01 AM

java object-oriented

Benefits and Usage of the Java Optional Class

TheJavaOptionalclassreducesnullpointerexceptionsbyexplicitlysignalingpotentialabsenceofvalues.1.UseOptional.of()fornon-nullvalues,Optional.ofNullable()forpossiblenulls,andOptional.empty()foremptyinstances.2.CheckpresencewithisPresent()orisEmpty(),ret

Jul 06, 2025 am 01:56 AM

How to use the ExecutorService in Java?

ExecutorService is an important tool in Java to manage thread execution tasks. You can create fixed-size thread pools, cache thread pools and single thread pools through the Executors factory class. 1. Submit the task using submit() or execute() method. Submit() can return the Future object to obtain the result or exception; 2. Process the return value and obtain the result through Future.get() blocking, or use invokeAll() to uniformly process the return value of multiple tasks; 3. Close the ExecutorService, you should first call shutdown() to stop receiving the new task and wait for completion. If the timeout, call shutdownNow()

Jul 06, 2025 am 01:44 AM

Implementing Lambda Expressions in Java.

Java8's Lambda expressions are implemented by simplifying anonymous internal classes, making the code more concise. 1. The basic syntax is (parameter list)->{ method body}, such as Runnabler=()->System.out.println("Hello"); 2. Commonly used for collection traversal and sorting, such as names.forEach(name->System.out.println(name)) and numbers.sort((a,b)->a.compareTo(b)); 3. It can only be used for functional interfaces, that is, interfaces with only one abstract method, such as Runnable

Jul 06, 2025 am 01:27 AM

Explain the concept of Java Native Interface (JNI).

JNI (JavaNativeInterface) is a framework that allows Java code to interact with local applications or libraries written in other languages ??such as C, C, or assembly. 1. Its main function is to serve as a bridge between Java and local code, so that Java can safely break through the isolation of JVM to access system resources; 2. Usage scenarios include calling high-performance mathematical libraries, connecting to platform-specific APIs, or encapsulating native SDKs; 3. The usage steps include declaring native methods, generating C/C header files, implementing and compiling into shared libraries, and loading the library in Java; 4. Notes include using JNI types for data type differences, operating Java objects must be done through JNI functions, and debugging.

Jul 06, 2025 am 01:11 AM

jni

Comparing Java HashMap and ConcurrentHashMap Performance

ConcurrentHashMapperformsbetterthanHashMapinmulti-threadedenvironmentsduetobuilt-inconcurrencysupport.1.HashMapisnotthread-safeandrequiresexternalsynchronization,leadingtooverhead.2.ConcurrentHashMapusessegmentlocking(Java7andearlier)orsynchronizedbi

Jul 06, 2025 am 01:09 AM

How Does Java HashMap Work Internally?

HashMap uses a hash algorithm to map keys to array indexes to achieve fast access. 1. First call hashCode() to get the hash value, and then determine the index position through perturbation function processing and modulo acquisition; 2. Use a linked list to resolve hash conflicts. After Java 8, the linked list will be converted into a red and black tree to improve search efficiency; 3. The load factor is 0.75 when expanding capacity, and if the threshold exceeds the rehashing value, it will be rehashing to expand the array capacity; 4. The initial capacity can be preset to reduce the number of expansions to improve performance.

Jul 06, 2025 am 12:22 AM

Purpose and Usage of the 'volatile' Keyword in Java

volatile is a lightweight synchronization mechanism in Java used to ensure variable visibility and orderliness. It is suitable for scenarios where variable changes need to be perceived in a timely manner in a multi-threaded environment. 1. It ensures that the thread reads the latest value of the variable and forces read and write to directly operate the main memory; 2. It prohibits instruction reordering and maintains the program execution order; 3. It does not guarantee atomicity and is not suitable for compound operations such as i. Common uses include status flags, one-time releases, and independent observation updates. When using it, you should cooperate with lock or CAS operations to avoid concurrent errors caused by misuse.

Jul 06, 2025 am 12:03 AM

Explained: Java Polymorphism in Object-Oriented Programming

Polymorphism is one of the core features of Java object-oriented programming. Its core lies in "one interface, multiple implementations". It implements a unified interface to handle the behavior of different objects through inheritance, method rewriting and upward transformation. 1. Polymorphism allows the parent class to refer to subclass objects, and the corresponding methods are called according to the actual object during runtime; 2. The implementation needs to meet the three conditions of inheritance relationship, method rewriting and upward transformation; 3. It is often used to uniformly handle different subclass objects, collection storage and framework design; 4. When used, only the methods defined by the parent class can be called. New methods added to subclasses need to be transformed downward and accessed, and pay attention to type safety.

Jul 05, 2025 am 02:52 AM

java Polymorphism

Implementing and Managing Thread Pools in Java

Java thread pools are created using ThreadPoolExecutor, and you need to pay attention to the core parameter configuration. 1. The number of core threads controls the number of resident threads. It is recommended to set it to the number of CPU cores for calculation-intensive tasks; 2. The maximum number of threads should deal with burst traffic, and excessively high will increase thread switching overhead; 3. The task queue size needs to weigh the risk of memory usage and task loss; 4. The rejection strategy can be customized, such as throwing an exception or executing by the caller; 5. Shutdown should be called first and then combined with awaitTermination and shutdownNow to ensure safe exit. Directly using the Executors tool class can easily cause memory overflow. The submit() method supports obtaining task results. Futur

Jul 05, 2025 am 02:50 AM

java Thread Pool

What is garbage collection in Java and how does it work?

Java's garbage collection (GC) is a mechanism for JVM to automatically manage memory. Its core role is to identify and clear objects that are no longer used to free memory. GC determines whether an object is useless through accessibility analysis. Common GCRoots include local variables in threads, static properties of the class, constant references and JNI references. JVM provides a variety of collectors, such as SerialGC, ParallelGC, CMSGC, G1GC, ZGC and ShenandoahGC, which are suitable for different scenarios. The garbage collection process usually includes three stages: marking, cleaning and sorting. Some collectors such as G1 divide the heap into multiple areas for flexible recycling. Developers can avoid frequent creation of temporary objects, set the heap size reasonably,

Jul 05, 2025 am 02:47 AM

Understanding the Java Virtual Machine Architecture

The JVM architecture consists of three core cores: class loader, runtime data area and execution engine; the class loader is responsible for loading .class files, the runtime data area includes heap, stack, etc. for storing data, and the execution engine is responsible for interpreting or compiling bytecode; the heap stores object instances in the runtime data area, the method area saves class information, and stack management method calls; the class loading mechanism includes three stages: loading, linking, and initialization, and follows the parent delegation model to ensure security; mastering these basic structures helps troubleshoot problems and optimize performance.

Jul 05, 2025 am 02:40 AM

What is Immutability and how to achieve it in Java?

Once an immutable class is created, its state cannot be modified, and any operation will return a new object. To implement immutable classes in Java, the following steps must be followed: 1. Declare the class as final; 2. Set all fields to private and final; 3. Only getter methods are provided, no setters are provided; 4. All fields must be initialized in the constructor; 5. For fields of mutable types, defensive copies are made during assignment and acquisition. In addition, Java 9 supports built-in immutable collections such as List.of(), etc., which helps reduce boilerplate code and prevents accidental modifications. As long as you pay attention to the design of the class and internal state protection, you can achieve true immutability in Java.

Jul 05, 2025 am 02:39 AM

java